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Tuesday, 4 December 2012

Tuesday, 20 November 2012

Felicity: Spatiotemporal characterization of few-cycle laser pulses

In this paper we apply a broadband fiber optic coupler interferometer to the measurement of few-cycle laser pulses. Sub-8-fs pulses delivered by an ultrafast oscillator were characterized spatiotemporally using STARFISH, which is based on spatially resolved spectral interferometry. The reference pulse was measured with the d-scan technique. The pulses were focused by an off-axis parabolic mirror and were characterized at different transverse planes along the focusing region. The evolution of the retrieved pulses is analyzed, exhibiting small variations in the temporal (and spectral) amplitude and phase during propagation. Finally, the peak irradiance evolution is estimated from the integration of the spatiotemporal intensity.

Tuesday, 6 November 2012

Marta: Laser Nanofabrication of Soft Matter

Laser based techniques constitute an advantageous versatile approach for the assembly and control at nanometer scale of polymers and biopolymers, fundamental components of soft matter. In this chapter lasernanostructuring of thin films of these materials will be illustrated by studies on laser induced periodic surface structures (LIPSS) and on laser foaming and on their respective application for surface enhanced Raman spectroscopy (SERS) based sensors and for scaffolds in tissue engineering.

Tuesday, 30 October 2012

Tuesday, 2 October 2012

Seb: Oriented Rotational Wave-Packet Dynamics Studies via High Harmonic Generation

Phys. Rev. Lett. 109, 113901 (2012) [5 pages]

Oriented Rotational Wave-Packet Dynamics Studies via High Harmonic Generation

No Citing Articles
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E. Frumker1,2,3,*C. T. Hebeisen1N. Kajumba1,4J. B. Bertrand1H. J. Wörner1,5M. Spanner6D. M. Villeneuve1A. Naumov1, and P. B. Corkum1,†
1Joint Attosecond Science Laboratory, University of Ottawa and National Research Council of Canada, 100 Sussex Drive, Ottawa, ON K1A 0R6, Canada
2Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany
3Department of Physics, Texas A&M University, College Station,Texas 77843, USA
4Department für Physik der Ludwig-Maximilians-Universität, Schellingstrasse 4, D-80799 Munich, Germany
5Laboratorium für physikalische Chemie, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland
6Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, ON K1A 0R6, Canada
Received 12 April 2012; published 12 September 2012
We produce oriented rotational wave packets in CO and measure their characteristics via high harmonic generation. The wave packet is created using an intense, femtosecond laser pulse and its second harmonic. A delayed 800 nm pulse probes the wave packet, generating even-order high harmonics that arise from the broken symmetry induced by the orientation dynamics. The even-order harmonic radiation that we measure appears on a zero background, enabling us to accurately follow the temporal evolution of the wave packet. Our measurements reveal that, for the conditions optimum for harmonic generation, the orientation is produced by preferential ionization which depletes the sample of molecules of one orientation.
Published by the American Physical Society
42.65.Ky, 07.57.-c

Tuesday, 25 September 2012

Simon:Wave packet theory of dynamic absorption spectra in femtosecond pump–probe experiments

J. Chem. Phys. 92, 4012 (1990); (18 pages)

Wave packet theory of dynamic absorption spectra in femtosecond pump–probe experiments

W. Thomas PollardSoo‐Y. Lee, and Richard A. Mathies
Department of Chemistry, University of California, Berkeley, California 94720 
(Received 18 July 1989; accepted 8 December 1989)

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The large spectral width of ultrashort optical pulses makes it possible to measure the complete time‐resolved absorption spectrum of a sample with a single pulse, offering simultaneously high resolution in both the time and frequency domains. To quantitatively interpret these experiments, we start with the usual perturbative density matrix theory for the third‐order susceptibility of a multilevel system. However, the theory is formulated in terms of four‐time correlation functions which are interpreted as the time‐dependent overlap of bra and ket vibrational wave packets propagating independently on the ground and excited electronic state potential surfaces. This approach captures the critical distinction between electronic population decay and pure dephasing processes, while retaining the intuitive physical picture offered by the time‐dependent wave packet theories of molecular spectroscopy. A useful simplification is achieved by considering the absorption of the probe pulse as the firstorder spectroscopy of the nonstationary state created by the pump pulse. In this case, the dynamic spectrum is obtained through the Fourier transform of the time‐dependent overlap of the initial wave packet propagating on its potential surface and a second wave packet, created by the probe pulse, which evolves simultaneously on the final surface. Calculations for model systems using harmonic surfaces and δ‐function pulses are presented to illustrate the application of this theory and to clarify the unique spectral behavior of the nonstationary states created in femtosecond pump–probe experiments. Finally, we demonstrate the practical application of the theory for anharmonic surfaces and finite pulses by analyzing the dynamic spectroscopy of the excited state torsional isomerization of the bacteriorhodopsin chromophore.

Tuesday, 18 September 2012

Sebastien: Attosecond Control of Orbital Parity Mix Interferences and the Relative Phase of Even and Odd Harmonics in an Attosecond Pulse Train

Phys. Rev. Lett. 109, 083001 (2012) [5 pages]

Attosecond Control of Orbital Parity Mix Interferences and the Relative Phase of Even and Odd Harmonics in an Attosecond Pulse Train

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G. Laurent*W. CaoH. LiZ. WangI. Ben-Itzhak, and C. L. Cocke
Physics Department, James R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506, USA
Received 19 March 2012; published 20 August 2012
We experimentally demonstrate that atomic orbital parity mix interferences can be temporally controlled on an attosecond time scale. Electron wave packets are formed by ionizing argon gas with a comb of odd and even high-order harmonics, in the presence of a weak infrared field. Consequently, a mix of energy-degenerate even and odd parity states is fed in the continuum by one- and two-photon transitions. These interfere, leading to an asymmetric electron emission along the polarization vector. The direction of the emission can be controlled by varying the time delay between the comb and infrared field pulses. We show that such asymmetric emission provides information on the relative phase of consecutive odd and even order harmonics in the attosecond pulse train.
© 2012 American Physical Society
32.80.Rm, 32.80.Qk, 42.65.Ky

Tuesday, 11 September 2012

Thomas: Theoretical study of photoelectron angular distributions in single-photon ionization of aligned N2 and CO2

Phys. Rev. A 81, 033421 (2010)

Theoretical study of photoelectron angular distributions in single-photon ionization of aligned N2 and CO2

the angular distribution of the momenta of XUV ionised electrons is going to bare much relevance to the XUV initiated HHG experiment which is being constucted in the basement at the moment. i would like to take this journal club as an opportunity to involve both theoreticians and experimentalists in a discussion about the differing properties of XUV and tunnel ionised electrons and how we can use these properties to our advantage. i would also like to discuss the possibilities of writing a ral proposal for attempting to measure the ion state resolved angular distribution of the emitted electrons. for experimentalists all that theory has been prompted by J. Phys. Chem. A2008, 112, 9382–9386.

Tuesday, 31 July 2012

Malte: Strong field quantum control in CO2 in (1+2+3) steps

The polarisation dependence of double ionisation in CO2 and dissociative excitation of the parent ion
has been investigated experimentally via laser induced impulsive alignment. For the ?first time, the
recollision contribution to these channels is identifi?ed unambiguously and resolved angularly. This
is achieved by employing an elliptically polarised probe pulse, which maintains a main polarisation
direction while switching of? recollision. It was found that tunnel-ionisation from lower lying orbitals
in the neutral and thus higher lying excited states in the parent ion are involved in all of the investigated
processes, even at relatively low intensities. While CO+ is formed almost exclusively via tunnel ionisation from HOMO-2 followed by strong ?field excitation, recollision was found to be a signi?cant channel for O+ production. A strong polarisation dependence in both channels enables varying the associated branching ratios and demonstrates the possibility of strong fi?eld quantum control via the laser polarisation.

Tuesday, 10 July 2012

Zara: Coupling between energy and phase in hollow-core fiber based f-to-2f interferometers

Journal club about the paper:

"Coupling between energy and phase in hollow-core fiber based f-to-2f interferometers "

also read:
"Determining the phase-energy coupling coefficient in carrier-envelope phase measurements"

Tuesday, 3 July 2012

Bridgette: Laser Enabled Auger Decay in Atoms and Molecules: Probing Electron Correlation in Inner-valence ionised States

Auger type decay processes play a fundamental role in atomic/molecular spectroscopy, sur-
face analysis, radiation damage, etc. These transitions can be viewed as consisting of two steps.
Firstly, a high energy photon produces a hole in an inner electronic shell, emitting a photoelec-
tron with kinetic energy dependent on the incident photon. Then the hole is lled by a valence
electron and a second valence electron is emitted with energy dependent on the energy levels of
the singly and doubly charged ions and not the incident photon energy. Auger decay processes
are considered to be an important manifestation of electron correlation as they are only possible
because of electron-electron interactions.

Recently, Murnane and Kapteyn [1] have investigated Laser-Enabled Auger Decay (LEAD)
in the multi-photon regime for vacancies that are not energetic enough to undergo the normal
Auger decay. Here we show that if considered in the single-photon regime, the LEAD process
provides a valuable insight into electron correlation in the inner valence ionised states. Firstly,
we analyse the single photon LEAD for the 2s-ionised state in Ne . A detailed investigation of
the mechanism of this single-photon LEAD process reveals that it is only possible because the
initial 2s-1 one-hole state contains con gurations of the type two holes and an electron excited
to a high-energy orbital. The cross-section of the single-photon LEAD process becomes a direct
measure of this con guration mixing. We use the rst-principles algebraic diagrammatic con-
struction (ADC) scheme and the Stieltjes imaging technique[2] to evaluate the single-photon
LEAD cross-sections in ns-ionised states of Ne and Ar. The correlation in the inner valence
ionised states of trans-1,3 Butadiene are investigated as they are an example of a molecule with
strong con guration mixing resulting in the breakdown of the molecular orbital (MO) picture
of ionisation[3]. We show that the breakdown of the MO picture leads to a dramatic increase
of the single-photon LEAD cross-section relative to the atomic case. Finally, we propose that
single photon LEAD can be a sensitive experimental probe for the attosecond hole migration
triggered by the MO breakdown.

1 P. Ranitovic, X. M. Tong, C. W. Hogle, X. Zhou, Y. Liu, N. Toshima, M. M. Murnane,
H. C. Kapteyn, Phys. Rev. Lett. 106, 053002 (2011).
2 See e.g. K. Gokhberg, V. Vysotskiy, L. S. Cederbaum, L. Storchi, F. Tarantelli, V. Averbukh,
J. Chem. Phys. 130, 064104 (2009).
3 L. S. Cederbaum, W. Domcke, J. Schirmer, W. Von Niessen, Adv. Chem. Phys. 65, 115

Tuesday, 19 June 2012

Amelle: Conical Intersection Dynamics in NO2 Probed by Homodyne High-Harmonic Spectroscopy

Conical Intersection Dynamics in NO2 Probed by Homodyne High-Harmonic Spectroscopy
  1. D. M. Villeneuve1
+Author Affiliations
  1. 1Joint Laboratory for Attosecond Science, National Research Council of Canada and University of Ottawa, 100 Sussex Drive, Ottawa, Ontario, Canada K1A 0R6.
  2. 2Laboratorium für Physikalische Chemie, Eidgenössische Technische Hochschule Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
  3. 3Centre Lasers Intenses et Applications, Université de Bordeaux, CEA, CNRS, UMR5107, 351 Cours de la Libération, 33405 Talence, France.
  4. 4Laboratoire Collisions Agrégats Réactivité (IRSAMC), UPS, Université de Toulouse, F-31062 Toulouse, France and CNRS, UMR 5589, F-31062 Toulouse, France
  1. *To whom correspondence should be addressed. E-mail:


Conical intersections play a crucial role in the chemistry of most polyatomic molecules, ranging from the simplest bimolecular reactions to the photostability of DNA. The real-time study of the associated electronic dynamics poses a major challenge to the latest techniques of ultrafast measurement. We show that high-harmonic spectroscopy reveals oscillations in the electronic character that occur in nitrogen dioxide when a photoexcited wave packet crosses a conical intersection. At longer delays, we observe the onset of statistical dissociation dynamics. The present results demonstrate that high-harmonic spectroscopy could become a powerful tool to highlight electronic dynamics occurring along nonadiabatic chemical reaction pathways.

Tuesday, 12 June 2012

Thomas Gaumnitz: Chirped Auger emission at FLASH reveals long-range electron correlation

The energy of Auger electrons, i.e. secondary electrons emitted after a non-radiative decay of a deeply bound electronic core-hole, is an intrinsic property of the electronic structure of the excited atom and does not directly rely on the energy of the exciting photon, electron or ion. The electron emission is not mono-energetic, though; the fast - attosecond to femtosecond - decay times imply corresponding spectral widths in a range of a few tens of meV to a few eV. This time-energy correspondence suggests a uniform distribution of all energy components over time. In this work, we demonstrate that under spectroscopically relevant conditions, this presumption is wrong. Instead, our time-resolved experiments show evidence of an energetic chirp, i.e. a pronounced time-dependent variation of the Auger-electrons´ kinetic energy. It appears as a consequence of the correlated motion of both photo- and Auger electrons in the Coulomb field of the remaining ion. While the underlying mechanism - also known as ‘post-collision interaction’ (PCI) - has extensively been discussed in the literature, no attention has so far been paid to the consequence of the effect for the temporal properties of the escaping electron wave packets. We visualize this temporal energy variation by superimposing 13.5nm XUV pulses from FLASH with the oscillating electric field of a strong terahertz (THz) wave from the FLASH THz undulator in a xenon gas-target. Significantly, modified widths of kinetic energy spectra for opposite field gradients clearly indicate a chirp (see Fig. 1).

Figure 1: Kinetic energy spectra of xenon Auger lines formed after absorption of XUV photons in the presence of a THz field. The modified widths of the Auger lines for opposite field gradients indicate an energy chirp.

The experiments have been confirmed in the laboratory where a high harmonics XUV source and a laser based THz source were employed. The observed spectral modulations are reproduced with semi-classical as well as  quantum simulations, and are explained by an analytical model, which includes PCI in the presence of a time-dependent streaking field.

Tuesday, 3 April 2012

Stefan: High-energy density laboratory astrophysics studies of accretion shocks in magnetic cataclysmic variables

In this paper we present the experimental simulation of the accretion column in magnetic cataclysmic variables using high-power lasers. With an appropriate target and adapted diagnostics, the dynamics and the main physical properties of laboratory accreting plasma have been characterised. The results obtained validate the experimental design and prove the formation of a reverse shock which compresses and heats the accreting plasma. The data are compared to 2D radiation hydrodynamic simulations, confirming the experimental scenario.

Tuesday, 13 March 2012

Marco + Leszek: Electron VMI / Extraction of correlations from covariance mapping

(1) Electron VMI (discussion led by Marco)

(2) On the requirements for extraction of correlations from covariance mapping (Leszek).

Tuesday, 6 March 2012

Matle+Seb: Characterising and optimising impulsive molecular alignment in mixed gas samples

Impulsive molecular alignment has been fully characterized in linear molecules by matching
numerical simulations and experimental data of the Fourier transformed time-evolution of the
corresponding rotational wavepacket. For this, a qualitative measure of the alignment distri-
bution is sufficient, making this a versatile procedure in experiments where the molecular axis
distribution is not directly accessible. Seeding small molecules in Ar as a carrier gas has then
been employed to assist cooling and we systematically retrieve the molecule’s rotational temper-
ature and alignment distribution for different mixing ratios. It was found that seeding 10% N2
in Ar results in the best cooling. Compared to pure N2 the rotational temperature was reduced
from 24 ± 2 K down to 9 ± 2 K. This leads to an improvement of the alignment distribution from
〈cos2 θ〉 = 0.60 to 〈cos2 θ〉 = 0.71. For the same mixing ratio CO2 was cooled from 34 ± 3 K

to 9 ± 1 K improving the alignment distribution from 0.48 to 0.64. In O2 a cooling from 58 ± 2
K to 37 ± 4 K was observed, corresponding to an alignment distribution improvement from 0.49
to 0.58. The results demonstrate the wide applicability of the characterisation procedure and of seeded supersonic beams to optimise impulsive alignment of small molecules.

Tuesday, 28 February 2012

Felicity: High-harmonic generation in H2O

We demonstrate high-harmonic generation in H2O using 800 and 1300nm laser pulses up to a maximum intensity of 5×1014W/cm2. Under optimal phase-matching conditions, photon energies up to ~60 and ~87 eV are produced by using 800 and 1300nm light, respectively. The harmonic spectra in H2O, when compared with Xe with a similar ionization potential, exhibit significant extension of the cutoff region, indicating suppression of ionization arising from molecular orbital symmetry.



Tuesday, 21 February 2012

Simon: Controlling the XUV Transparency of Helium Using Two-Pathway Quantum Interference

Atoms irradiated with combined femtosecond laser and extreme ultraviolet (XUV) fields ionize through
multiphoton processes, even when the energy of the XUV photon is below the ionization potential.
However, in the presence of two different XUV photons and an intense laser field, it is possible to induce
full electromagnetic transparency. Taking helium as an example, the laser field modifies its electronic
structure, while the presence of two different XUV photons and the laser field leads to two distinct
ionization pathways that can interfere destructively. This work demonstrates a new approach for coherent
control in a regime of highly excited states and strong optical fields.

sildes here:

Tuesday, 7 February 2012

Richard: Atomic inner-shell X-ray laser at 1.46 nanometres pumped by an X-ray free-electron laser

Atomic inner-shell X-ray laser at 1.46 nanometres pumped by an X-ray free-electron laser

Since the invention of the laser more than 50 years ago, scientists have striven to achieve amplification on atomic transitions of increasingly shorter wavelength1, 2, 3, 4, 5, 6, 7. The introduction of X-ray free-electron lasers8, 9, 10makes it possible to pump new atomic X-ray lasers11, 12, 13 with ultrashort pulse duration, extreme spectral brightness and full temporal coherence. Here we describe the implementation of an X-ray laser in the kiloelectronvolt energy regime, based on atomic population inversion and driven by rapid K-shell photo-ionization using pulses from an X-ray free-electron laser. We established a population inversion of the Kα transition in singly ionized neon14at 1.46 nanometres (corresponding to a photon energy of 849 electronvolts) in an elongated plasma column created by irradiation of a gas medium. We observed strong amplified spontaneous emission from the end of the excited plasma. This resulted in femtosecond-duration, high-intensity X-ray pulses of much shorter wavelength and greater brilliance than achieved with previous atomic X-ray lasers. Moreover, this scheme provides greatly increased wavelength stability, monochromaticity and improved temporal coherence by comparison with present-day X-ray free-electron lasers. The atomic X-ray lasers realized here may be useful for high-resolution spectroscopy and nonlinear X-ray studies.

Additional Info:

Tuesday, 31 January 2012

Seb: Hollow core fiber at 1.8microns

Trallero-Herrero, C., Jin, C., Schmidt, B. E., Shiner, a D., Kieffer, J.-C., Corkum, P. B., Villeneuve, D. M., et al. (2012). Generation of broad XUV continuous high harmonic spectra and isolated attosecond pulses with intense mid-infrared lasers. Journal of Physics B: Atomic, Molecular and Optical Physics, 45(1), 011001. doi:10.1088/0953-4075/45/1/011001

Shiner, a. D., Schmidt, B. E., Trallero-Herrero, C., Wörner, H. J., Patchkovskii, S., Corkum, P. B., Kieffer, J.-C., et al. (2011). Probing collective multi-electron dynamics in xenon with high-harmonic spectroscopy. Nature Physics, 7(6), 464-467. Nature Publishing Group. doi:10.1038/nphys1940
supplementary information (a lot of material):

Tuesday, 10 January 2012

DM: Simon: XUV Initiated High Harmonic Generation

I intend on giving a thorough and descriptive introduction so if you'd like to learn more about what I'm trying to do in my project - this would be a good opportunity to find out! Also, if you think that your wisdom might add to the discussion, please come along - as I would value external insight.